Outcomes by molecular subtype after accelerated partial breast irradiation using single-entry catheters

Area of Science:

• Oncology
• Radiation Oncology
• Breast Cancer Research

Background:

• Tumor biology is increasingly recognized as a critical factor influencing prognosis and the risk of locoregional recurrence in breast cancer.
• Understanding recurrence rates based on molecular subtypes is essential for optimizing treatment strategies, particularly for accelerated partial breast irradiation (APBI).

Purpose of the Study:

• To determine and compare actuarial recurrence rates based on approximated molecular subtypes in women treated with single-entry catheter accelerated partial breast irradiation (sAPBI).
• To evaluate the efficacy of sAPBI in managing different breast cancer subtypes, including Luminal A, Luminal B, Her2-positive, and triple-negative breast cancer (TNBC).

Main Methods:

• A retrospective analysis of 1,486 women with invasive breast cancer treated with MammoSite, Contura, or SAVI sAPBI between 2002 and 2014.
• Patients' ER, PR, and Her2 status were known, and follow-up was at least 1 year.
• Actuarial recurrence rates were calculated using the Kaplan-Meier method for four approximated molecular subtypes: Luminal A (n=1081), Luminal B (n=164), Her2 (n=123), and TNBC (n=118).

Main Results:

• The overall 5-year in-breast tumor recurrence rate was 2.6%, with rates of 2.1% for Luminal A, 1.5% for Luminal B, 4.9% for Her2, and 5.4% for TNBC.
• Luminal A and B subtypes showed significantly lower 5-year in-breast tumor recurrence rates (2.1%) compared to the combined Her2 and TNBC subtypes (5.1%, p=0.021).
• The 5-year locoregional control was 97.3% for Luminal cancers and 93.8% for the combined Her2 and TNBC subtypes.

Conclusions:

• Single-entry catheter accelerated partial breast irradiation (sAPBI) demonstrates excellent 5-year locoregional control for Luminal breast cancers.
• While sAPBI shows promise, patients with more aggressive Her2 and TNBC subtypes experienced higher recurrence rates, suggesting a need for caution.
• Further randomized trials are necessary to establish the optimal treatment approach for higher-risk breast cancer subtypes like Her2 and TNBC.